No abstract

Much evidence suggests that life originated in hydrothermal habitats, and for much of the time since the origin of cyanobacteria (at least 2.5 Ga ago) and of eukaryotic algae (at least 2.1 Ga ago) the average sea surface and land surface temperatures were higher than they are today. However, there have been at least four significant glacial episodes prior to the Pleistocene glaciations. Two of these (approx. 2.1 and 0.7 Ga ago) may have involved a 'Snowball Earth' with a very great impact on the algae (sensu lato) of the time (cyanobacteria, Chlorophyta and Rhodophyta) and especially those that were adapted to warm habitats. By contrast, it is possible that heterokont, dinophyte and haptophyte phototrophs only evolved after the Carboniferous-Permian ice age (approx. 250 Ma ago) and so did not encounter low (

Polar seaweeds are strongly adapted to the low temperatures of their environment, Antarctic species more strongly than Arctic species due to the longer cold water history of the Antarctic region. By reason of the strong isolation of the Southern Ocean the Antarctic marine flora is characterized by a high degree of endemism, whereas in the Arctic only few endemic species have been found so far. All polar species are strongly shade adapted and their phenology is finely tuned to the strong seasonal changes of the light conditions. The paper summarises the present knowledge of seaweeds from both polar regions with regard to the following topics: the history of seaweed research in polar regions; the environment of seaweeds in polar waters; biodiversity, biogeographical relationships and vertical distribution of Arctic and Antarctic seaweeds; life histories and physiological thallus anatomy; temperature demands and geographical distribution; light demands and depth zonation; the effect of salinity, temperature and desiccation on supraand eulittoral seaweeds; seasonality of reproduction and the physiological characteristics of C. Wiencke (&) AE U. H. Lü der

No abstract

Summary 1The UV susceptibility of zoospores of the brown seaweeds Saccorhiza dermatodea , Alaria esculenta and Laminaria digitata (Laminariales) was determined in field experiments in June 2004 on Spitsbergen (78 ° 55 ′ N, 11 ° 56 ′ E). 2 Freshly released zoospores were exposed for 1 or 2 days at various water depths to ambient solar radiation, ambient solar radiation depleted of UVB radiation (UVBR) and ambient solar radiation depleted of both UVBR and UVAR. Subsequently, germination rates were determined after exposure to favourable light and temperature conditions in the laboratory. 3 The radiation regime was monitored at the water surface and in the water column using data loggers attached adjacent to each experimental platform for the duration of the field exposure. 4 Under ambient solar radiation, the tolerance of zoospores to UVR was highest in the shallow water species S. dermatodea , intermediate in the upper to mid sublittoral A. esculenta and lowest in the upper to mid sublittoral L. digitata . There was, however, no difference in the susceptibility of the zoospores to ambient solar radiation or to solar radiation depleted of UVBR. 5 The water column was relatively UV transparent, especially in the upper water layers. The 1% UVB depth ranged between 5.35 and 6.87 m, although on one stormy day the 1% UVB depth was only 3.57 m, indicating resuspension of sediments. 6 Early developmental stages are most susceptible to environmental stress. Tolerance of zoospores to UVR is a major if not one of the most important factors determining the upper distribution limit of different Laminariales on the shore. 7 Kelps are very important primary producers in inshore coastal ecosystems, serving as food for herbivores and as habitat for many organisms. Enhanced UVBR due to stratospheric ozone depletion may lead to changes in the depth distribution of kelps and may cause significant ecological domino effects.